Re: [Intel-gfx] [PATCH] drm/i915/dsi: Explicit first_line_bpg_offset assignment for DSI

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 07 Aug 2023, Suraj Kandpal <suraj.kandpal@intel.com> wrote:
> Assign explicit value of 12 at 8bpp as per Table E2 of DSC 1.1 for DSI
> panels even though we already use calculations from CModel for
> first_line_bpg_offset.
> The reason being some DSI monitors may have not have added the
> change in errata for the calculation of first_line_bpg_offset.
>
> Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/icl_dsi.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/icl_dsi.c b/drivers/gpu/drm/i915/display/icl_dsi.c
> index f7ebc146f96d..2376d5000d78 100644
> --- a/drivers/gpu/drm/i915/display/icl_dsi.c
> +++ b/drivers/gpu/drm/i915/display/icl_dsi.c
> @@ -1585,6 +1585,11 @@ static int gen11_dsi_dsc_compute_config(struct intel_encoder *encoder,
>  	if (ret)
>  		return ret;
>  
> +	/* From Table E-2 in DSC 1.1*/
> +	if (vdsc_cfg->dsc_version_minor == 1 &&
> +	    vdsc_cfg->bits_per_pixel == 128)

So, vdsc_cfg->bits_per_pixel has 4 fractional bits, and that's 8 bpp
compressed?

Better describe it that way, instead of as 128.

But... looking around, in intel_vdsc.c we set:

	pps_val |= DSC_BPP(vdsc_cfg->bits_per_pixel);

and we have:

	#define DSC_BPP(bpp)	((bpp) << 4)

however, when reading it back in intel_dsc_get_config(), it's just
directly:

	vdsc_cfg->bits_per_pixel = pps1;

Are we always sending x16 bpp in PPS?


BR,
Jani.



> +		vdsc_cfg->first_line_bpg_offset = 12;
> +
>  	/* DSI specific sanity checks on the common code */
>  	drm_WARN_ON(&dev_priv->drm, vdsc_cfg->vbr_enable);
>  	drm_WARN_ON(&dev_priv->drm, vdsc_cfg->simple_422);

-- 
Jani Nikula, Intel Open Source Graphics Center